In AC color PDP devices, an address/display separation (ADS) method in which a period when the cells to be displayed are determined (address period) and a display period when discharges for display lighting are performed (sustain period) are separated is widely employed. In this method, charge is accumulated in the cells, which are to be turned on, in the address period, and discharges for display are performed by utilizing the charge in the sustain period.
Also, plasma display panels include: a two-electrode type PDP in which a plurality of first electrodes extending in a first direction are provided in parallel to each other and a plurality of second electrodes extending in a second direction which is perpendicular to the first direction are provided in parallel to each other; and a three-electrode type PDP in which a plurality of first electrodes and second electrodes extending in a first direction are alternately provided in parallel to each other and a plurality of address electrodes extending in a second direction perpendicular to the first direction are provided in parallel to each other. In recent years, the three-electrode type PDPs have been widely used.
In a general structure of the three-electrode type PDPs, first (X) electrodes and second (Y) electrodes are alternately provided in parallel to each other on a first substrate, address electrodes extending in a direction which is perpendicular to the extending direction of the first and second electrodes are provided on a second substrate opposite to the first substrate, and the surfaces of the electrodes are covered by dielectric layers. On the second substrate, barrier ribs which are extending in one direction and arranged in stripes between the address electrodes in parallel to the address electrodes or barrier ribs which are arranged in lattice pattern and disposed in parallel to the address electrodes and the first and second electrodes so as to individually separate the cells are further provided, and the first and the second substrates are attached to each other after phosphor layers are formed between the barrier ribs. Therefore, the dielectric layers and the phosphor layers and further the barrier ribs are formed on the address electrodes.
Discharges are caused in all of the cells by applying voltage between the first and second electrodes to make the charge (wall charge) in the vicinity of the electrodes uniform. Then, the addressing for selectively leaving the wall charge in the cells to be turned on is performed by sequentially applying scan pulses to the second electrodes and applying address pulses to the address electrodes in synchronization with the scan pulses. Subsequently, sustain discharge (sustain) pulses of potentials of alternately changed polarities are applied between the two adjacent first and second electrodes where discharges are to be performed. By doing so, the sustain discharges are performed in the cells to be turned on in which the wall charge has been formed through the addressing, thereby performing the lighting. The phosphor layers emit light by ultraviolet rays generated through the discharges, and the light is seen through the first substrate. Therefore, the first and second electrodes are comprised of non-transparent bus electrodes formed of metal materials and transparent electrodes such as ITO films, and the light generated in the phosphor layers can be seen through the transparent electrodes. Since structures and operations of general PDPs are widely known, detailed descriptions thereof will be omitted here.
In the field of the above-described three-electrode type PDP, various types of PDPs in which third electrodes are respectively provided between the first electrodes and the second electrodes in parallel thereto have been proposed.
For example, Japanese Patent Application Laid-Open Publication No. 2000-123741 (Patent Document 1) discloses a PDP device which performs interlaced display by utilizing display lines between first electrodes and third electrodes and between second electrodes and third electrodes.
Furthermore, Japanese Patent Application Laid-Open Publication No. 2001-34228 (Patent Document 2) and No. 2004-192875 (Patent Document 3) disclose the structure in which third electrodes are provided between first electrodes and second electrodes where discharge is not performed (non-display line) so that the third electrodes are utilized for trigger operations, prevention of discharges in non-display lines (prevention of reverse slit), reset operations, and others.
In general, the three-electrode type PDPs merely control lighting and non-lighting, and it is difficult to carry out grayscale display by precisely changing the light emission intensity. Therefore, in PDP devices, one display field is comprised of a plurality of sub-fields in general, and the grayscale display is carried out by combining the lighting sub-fields. The grayscales which can be displayed in this case correspond to combinations of luminance of the sub-fields. For example, if 8 sub-fields in which a luminance ratio is sequentially changed in the powers of 2 are provided, display of 256 grayscales can be carried out. Although this sub-field structure is the most efficient structure in terms of the relation between the number of sub-fields and the number of grayscales which can be displayed, it has a problem of, for example, the color drift and edge distortion. Therefore, various sub-field structures for reducing the color drift and edge distortion have been proposed.
Meanwhile, Japanese Patent Application Laid-Open Publication No. 2003-337566 (Patent Document 4) discloses a structure in which second (Y) electrodes are sorted into primary second electrodes and auxiliary second electrodes which are selectively used, and by selecting the second electrode to be used, the discharge area can be changed in each display line so as to change the luminance. When this structure is applied to the sub-field structure, the number of grayscales which can be displayed is increased.
Meanwhile, in PDP devices, it is desired to improve luminance (light emission amount) so as to obtain high display luminance. Therefore, in general, the total number of sustain pulses in sub-fields of one field, i.e., the number of total sustain pulses in one field is set as the maximum value. However, when the bright display is carried out on the entire screen, the amount of currents (electric power) fed to the entire panel increases, and the panel temperature increases to exceed a permissible value. Therefore, in such a case, power control for reducing the number of total sustain pulses in one field is performed. When the number of total sustain pulses is reduced, the numbers of sustain pulses are allotted to each of the sub-fields in accordance with the luminance ratio. However, the minimum number of total sustain pulses for accurately allotting the numbers of sustain pulses to the sub-fields in accordance with the luminance ratio is fixed, and if the number of total sustain pulses at that point is not an integral multiple of the minimum number of total sustain pulses, the numbers of sustain pulses cannot be accurately allotted to the sub-fields in accordance with the luminance ratio, and some errors occur in the luminance ratio.
Note that the number of total sustain pulses in one field is changed not only for the above-described power control but also for the prevention of local temperature increase in a still image and the like.